The system and method of the present invention pertains to controlling the process by which a transmission which connects a power source and a driven device, such as a pump, changes or shifts gear ratios. More particularly, the disclosed system and method may be used for any equipment powered by an engine, a motor, or a similar device that transfers rotating power through a geared transmission mechanism to obtain a rotating power output from the transmission for use by the equipment.
In oil well stimulation, fluid is pumped into the well to increase the production of hydrocarbons from the well bore. The success or failure of a well stimulation operation depends on the ability to closely control well bore pressures and the flow rate of the stimulation fluid pumped into the well. The requirements for the control of well bore pressures and the control of the flow of stimulation fluid into the well are such that during the stimulation treatment of some oil wells, even a small reduction in the flow of stimulation fluid into the well may significantly hamper well stimulation efforts.
Given the constraint of not reducing the flow of stimulation fluid into the well, the transmission connecting the power source, such as an engine or an electric motor, to the pump for the stimulation fluid is typically shifted during high output levels of the stimulation fluid pump in prior art systems. This shifting of the transmission at high power levels is detrimental to the inner workings of the transmission. Specifically, shifting of the transmission at high power levels often results in the premature failure of the transmission due to torque spikes in the drive train elements and excessive wear on the friction elements on the power train portion of the system.
Currently, there are no systems currently available for managing the shifting or the changing of the gear ratios in the transmission in large industrial applications such as oil well stimulation.
There is therefore a need in the art for a transmission shifting system which will allow shifting at other than high power levels but, at the same time, will allow driven items, such as pumps, to maintain a substantially continuous output.
The system and method of the present invention will allow shifting or changing the gear ratios in the transmission which connects a power source, such as an engine or an electric motor, and a driven device, such as a pump, at other than high power output levels without a substantial diminution of the output of the driven device.
The disclosed soft shift transmission shift and method alters the output rpm of the power source during the changing of gear ratios in the transmission to reduce wear on the gears and other transmission components. This alteration in the output rpm of the power source occurs when the driven device is decoupled from the power source such that the rpm of the power source is synchronized with the speed of the transmission output shaft as modified by the selected gear ratio. Once the synchronization of the rpm of the power source is synchronized with the speed of the transmission output shaft as modified by the selected gear ratio, the power source is re-coupled to the driven device at a lower energy value.
Operationally, the system and method of the present invention allows the transmission to enter its torque converter mode during the shift process. By allowing the transmission to enter its torque converter mode during the shift process, wear on the components within the transmission is reduced. This reduction in wear increases the serviceable life of the transmission and reduces operating costs without any substantial diminution in the performance of the driven device.